Various aspects of the individual steps of the multiple step process of this invention are known in the art, and various aspects appear to be new, useful, and not obvious. However, no reference could be located that describes the combination of process steps disclosed herein to super-purify smoke by removing the high quantity of particulate matter and taste imparting vapors necessary to produce a substantially tasteless smoke that will not impart a smoked taste to treated food.
Dating back thousands of years, before the invention of refrigeration, freezing and canning processes, various foods were cured by natural smoke. Natural smoke can preserve the nutritional components and wholesomeness of meats and seafood, while at the same time retarding spoilage. Smoked meats such as ham, bacon, beef jerky, sausage, poultry and smoked seafood are all examples of popular foods treated by smoke. The shelf life of meats can be extended to over one year (without refrigeration) by smoking. The taste of sausage and the color of ham are enhanced by smoking.
Following the invention of refrigeration, the vitality of whole or filleted seafood and other meats have been prolonged by maintaining the foods in cold storage of 28 to 40 degrees Fahrenheit (-2 to 5 degrees Centigrade). Seafood, in particular, in its raw state begins decomposition quickly at temperatures above 50 degrees Fahrenheit (10 degrees Centigrade). Seafood can be maintained fresh and unfrozen for up to two to three weeks at temperatures of 27 to 32 degrees Fahrenheit (-3 to 0 degrees Centigrade) due to the salt content in the meat. However, decomposition is inevitable and rapid after this time period and other methods of freezing, canning, and smoking have been necessary to extend the shelf life of the food.
Many types of smoking have been taught over the years to produce a variety of effects. Hot smoke will cook, dry, and dehydrate the flesh. Cold smoke will keep the meat moist and succulent. Components of the smoke emitted from various types of fuel will enhance the taste and preserve the color of the food. The combinations and variations in temperature from sub-freezing to over 200 degrees Fahrenheit (111 degrees Centigrade), fuel types, humidity, circulation and exposure times are great. In every case prior to this invention the result has been a smoke flavored food.
On Jun. 18, 1991, the Association of Food and Drug Officials, a national U.S. public sector organization, adopted a model code prepared by its Retail Food Subcommittee entitled "Good Manufacturing Practices for Cured, Salted, and Smoked Fish Establishments." Section 5.4 (a) (2) of this model code states that "The temperature in the smoking chamber does not exceed 50 degrees Fahrenheit (10 degrees Centigrade) during a drying and smoking period that does not exceed 24 hours," . . .
The longer the smoking period in this model code, the lower the maximum smoking temperature. For smoking periods of 30 to 48 hours the maximum smoking temperature declines to as low as 32 degrees Fahrenheit (0 degrees Centigrade). Thus, it has been established since 1991 that maximum cold smoking temperatures for smoking periods of 24 to 48 hours can vary from 32 to 50 degrees Fahrenheit (0 to 10 degrees Centigrade) in order to keep the meat moist, succulent, and free from bacterial degeneration or contamination.
Cold smoking is an obvious choice for fresh seafood which normally requires constant cold storage to slow down decomposition and discoloration as evidenced by Section 4.1 (c) of this model code which states "Fresh fish, except those to be immediately processed, shall be iced or otherwise refrigerated to an internal temperature of 38 degrees Fahrenheit or below (3 degrees Centigrade or below) upon receipt and shall be maintained at that temperature until the fish are to be processed."
Section 4.2 states that "all operations involving the receiving, holding, processing and packaging of processed fish shall be conducted utilizing clean and sanitary methods and shall be conducted as rapidly as practical and at temperatures that will not cause any material increase in bacterial or other micro organic content or any degeneration or contamination of such processed fish." In addition, the 1994 U.S. Food and Drug Administration (F.D.A.) Fish and Fishery Products Hazards and controls Guide recommends a thorough organoleptic examination of seafood product that exceeds 40 degrees Fahrenheit (4.4 degrees Centigrade) at any time during processing.
In 1989 Alkar Inc. of Wisconsin designed and built a laboratory smokehouse for Iowa State University with specifications allowing for smoking at temperatures as low as 32 degrees Fahrenheit (0 degrees Centigrade). In this design Alkar utilized a refrigeration coil inside the smoking chamber to cool the smoke down and maintain it at these low temperatures. Subsequent commercial smokehouses throughout the industry have been outfitted with return air ducts with cooling coils to allow for cold smoking of fresh fish at temperatures specified in the model code above.
Furthermore, smokehouses have equipment for purifying the smoke during, and at the exhaust, of the smoking process. In 1995 Alkar presented a paper entitled "An Overview of Air Pollution Control Equipment for Smokehouses" and described all current types of exhaust control equipment divided into two major classes--particulate collection equipment, and gaseous control equipment. Particulate collection equipment includes electrostatic precipitators, venturi scrubbers, and ionizing wet scrubbers. Gaseous control equipment includes absorption systems such as packed columns and incinerators.
U.S. Pat. No. 5,484,619 to Yamaoka et al discloses a method and apparatus that use extra low temperature smoking of fish and meat to sterilize and prevent decomposition and discoloration while imparting an agreeable smoked taste and smell.
U.S. Pat. No. 889,828 to Trescott discloses a device for curing edible matter comprised of a curing apartment, a smoke supply source, and a combined smoke cooling, purifying, and drying chamber where a portion of moisture and carbon soot condenses on the walls of the chamber. Trescott's method and apparatus, as with Yamaoka's, utilizes partially purified smoke containing odor and taste imparting particulate matter and vapors flowing freely in contact with the edible matter, imparting a smoke flavored taste.
U.S. Pat. No. 4,522,835 to Woodruff et al teaches a method of maintaining redness in fish and red meat by first subjecting such fish or meat to an oxygen deprived atmosphere and then exposing the fish or meat to a modified atmosphere containing a small amount of carbon monoxide. Industrially manufactured carbon monoxide gas is produced using caustic chemicals and can contain toxic impurities. Treatment of seafood or meats with carbon monoxide gas is therefore prohibited by the U.S. F.D.A. and the Japan Ministry of Public Health.
U.S. Pat. No. 3,122,748 to Beebe relates to a method of treating red meat with carbon monoxide to achieve the appearance of meat that has been freshly cut. As with Woodruff, Beebe's method utilizes a gas that is prohibited for such use in the U.S. and Japan. Conversely, treatment of seafood, poultry, or meat with a natural smoking process is generally recognized as safe (GRAS) by the U.S. F.D.A. and the Japan Ministry of Public Health.
Soviet Patent SU 847973 to Kichkar, Nasibov, and Bunin discloses a method for the cold curing of fish products by stabilizing the temperature and velocity of the smoke in a smoking chamber kept in a range of approximately 32 to 36 degrees Fahrenheit (0 to 2 degrees Centigrade). Kichkar et al's cold smoking process results in phenol levels rising in the body of salmon more quickly than earlier methods reducing processing time and producing quality smoked taste, color, and preservative characteristics.
German Patent DE 3826211 to Schich teaches a smoking process using a condenser cooled filtered smoke. Smoke from a smoke generator is passed through a cooling condenser maintained at 5 to 14 degrees Fahrenheit (-10 to -15 degrees Centigrade) to form a condensate of carbon, other suspended materials, tar and gum which is discharged. Schich's method removes substantially all tar, pollutants and carcinogens and does not impact the taste and aroma imparting ingredients in the smoke.
The burning of wood sawdust, in an oxygen restricted retort has been empirically discovered to be the most efficient way to produce high quality smoke from an organic material. However, other organic materials such as leaves, bagasse from sugar cane, pineapple husks, and rice hulls can all be used successfully to produce a volume of smoke in any substantially oxygen free chamber at a lesser amount than the volume achieved from burning wood sawdust in a retort.
The smoke produced from burning wood and other organic material fuels is a function of combustion temperature and amount of air intake. FIG. 1 shows the composition of wood smoke emissions at varying combustion temperatures. The formation of deleterious polycyclic aromatic hydrocarbons (PAHS), and oxidation of organic vapors, including both condensable organic compounds as well as volatile organic compounds (VOCs) can be prevented by combusting below 850 degrees Fahrenheit (454 degrees Centigrade). If wood is combusted above this temperature level and these compounds are formed, they can be successfully filtered later in the process.
To minimize formation of these compounds and to conform to empirical data from our laboratory tests, an operable combustion temperature range of 400 to 950 degrees Fahrenheit (204 to 510 degrees Centigrade), a preferred range of 500 to 800 degrees Fahrenheit (260 to 571 degrees Centigrade), and an optimal range of 650 to 750 degrees Fahrenheit (343 to 399 degrees Centigrade) are established for the process described herein.
Typical wood fuels for smoking contain primarily a hydrocarbon composition of hydrogen and carbon along with other elements of sulfur, nitrogen, oxygen, and ash compounds of silicon dioxide, ferrous trioxide, titanium dioxide, aluminum trioxide, manganese tetrioxide, calcium oxide, magnesium oxide, sodium oxide, potassium oxide, sulfur dioxide, and chloride as shown in Table is
TABLE 1 ______________________________________ TYPICAL WOOD FUEL CHEMICAL ANALYSIS Oak Spruce Chips Chips ______________________________________ Analysis (dry basis), % by weight Proximate Volatile matter 76.0 69.5 Fixed carbon 18.7 26.6 Ash 5.3 3.8 Ultimate Hydrogen 5.4 5.7 Carbon 49.7 51.8 Sulfur 0.1 0.1 Nitrogen 0.2 0.2 Oxygen 39.3 38.4 Ash 5.3 3.8 Heating value, Btu/lb 8,370 8,740 Ash Analysis % by wt SiO.sub.2 11.1 32.0 Fe.sub.2 0.sub.3 3.3 6.4 TiO.sub.2 0.1 0.6 Al.sub.2 O.sub.3 0.1 11.0 Mn.sub.3 O.sub.4 Trace 1.5 CaO 64.5 25.3 MgO 1.2 4.1 Na.sub.2 O 8.0 8.0 K.sub.2 O 0.2 2.4 SO.sub.3 2.0 2.1 Cl Trace Trace ______________________________________
Source: "Wood residue--fired steam generator particulate matter control technology assessment, U.S. E.P.A., 1978.
The smoke produced from burning wood and other organic material fuels contains water vapor, CO.sub.2, CO, CH.sub.4 (methane); tiny particulates of creosote, tar, soot, and trace elements; and over 390 microscopic compounds occurring in either, or both, particulate and gaseous (vapor) phases. Larson and Koenig compiled "A Summary of the Emissions Characterization and Noncancer Respiratory Effects of Wood Smoke" in 1993. Table 2 from this report summarizes all the reported constituents in wood smoke and the ranges of their emission rates.
CO.sub.2, CO, NO.sub.2, NO, and monoaromatic phenols constituents in wood smoke all have preservative effects on treated seafood and meat. CO.sub.2 is the preservative of choice in modified atmosphere packaging of fresh seafood as it is easily absorbed into the meat displacing oxygen and inhibiting bacterial growth. Phenols, which are present in much smaller amounts than CO.sub.2, operate similarly as bacteria inhibitors. CO, NO.sub.2, and NO undergo chemical reactions with myoglobin to retard decomposition.
The invention described herein is primarily concerned with super-purifying smoke to eliminate the flavor and aroma components of both the smoke and the seafood or meat subsequently treated. Maga compiled a comprehensive review of the literature in 1988 in "Smoke in Food Processing." In this review, he cites thirteen researchers who conclude that the most important flavor components of smoke are monoaromatic phenols occurring in both the particulate and gaseous vapor phases.
The phenolic particulate phase has lower odor and taste recognition thresholds than the gaseous vapor phase indicating that a smaller quantity of particulate is required to produce the same level of smoke odor and taste as the gaseous vapor phase. The particulate phase also contains high levels of undesirable pollutants including tar, soot, ash, and char which are desirably filtered.
Therefore, it is typical in smoking of foods to filter pollutants from the phenolic particulate phase while retaining the gaseous vapor phase for characteristic smoke flavoring. The amounts of tar, soot, ash, char and other microscopic particulates have been filtered and minimized by many methods in current practice including tar settling systems, baffling systems, and washing systems in the line from the smoke generator to the smoking chamber. In addition, cooling and storage reduces the concentrations of phenolic particulate through settling. Some of these filtering methods remove substantially all the tar and particulate from wood smoke leaving only the gaseous vapor phase which produces the characteristic smoke flavor.
Daun isolated the phenolic fraction from both the vapor and particulate phases of wood smoke and through dilution determined, with the aid of a sensory panel, their recognition threshold and most desirable concentration for both odor and taste sensations. These data are summarized in Table 3.
Yamaoka et al claim a smoking method comprising a step "passing the produced smoke through a filter to remove mainly tar." Such tar filters are standard elements in smoke generating systems sold today. However, since the flavor producing, monaromatic phenols in the gaseous vapor phase remain, Yamaoka's method imparts an "agreeable taste and smell" and does not produce tasteless smoke or tasteless food as does the process described herein.
Kichkar et al achieve up to 304 milligrams of phenols combined from both the particulate and gaseous vapor phases of wood smoke absorbed into the body of a salmon of approximately five kilograms, or 60.8 parts per million (ppm). This is the desirable concentration for quality smoked taste. Since the invention described herein is concerned with eliminating any flavor or aroma imparted to the treated seafood or meat, we have determined empirically that the recognition threshold for phenols in seafood or meat is approximately 9.4 ppm. However, even if the phenols in the seafood or meat are below this recognition threshold, they still exert positive preservative effects as bacteria inhibitors.
TABLE 2 ______________________________________ CHEMICAL COMPOSITION OF WOOD SMOKE Species 1 g/kg wood 2 Physical State 3 Reference ______________________________________ Water Vapor 35-105 v 2 Carbon Dioxide 70-200 v 2 Carbon Monoxide 80-370 v 4,5 Methane 14-25 v 5 VOCs (C2-C&) 7-27 v 5 Aldehydes 0.6-5.4 v 4,6 Formaldehyde 0.1-0.7 v 4,6 Acrolein 0.02-01 v 6 Propionaldehyde 0.1-0.3 v 4,6 Butryaldehyde 0.01-1.7 v 4,6 Acetaldehyde 0.03-0.6 v 4,6 Furfural 0.2-1.6 v 7,8 Substituted Furans 0.15-1.7 v 5 Benzene 0.6-4.0 v 9 Alkyl Benzenes 1-6 v 9 Toluene 0.15-1.0 v 7 Acetic Acid 1.8-2.4 v 7 Formic Acid 0.06-0.08 v 4,5 Nitrogen Oxides 0.2-0.9 v 4 (NO, NO2) Sulfur Dioxide 0.16-0.24 v 10 Methyl chloride 0.0-0.04 v 9 Napthalene 0.24-1.6 v 9 Substituted 0.3-2.1 v/P 9 Napthalenes Oygenated 1-7 v/P 11 Monoaromatics Guaiacols 0.4-1.6 v/P 11 Phenols 0.2-0.8 v/P 11 Syringols 0.7-2.7 v/P 11 Catechols 0.2-0.8 v/P 5 Total Particulate 7-30 P 12 Mass Oxygenated PAHs 0.15-1.0 v/P 13 PAHS Fluorene 0.00004-0.017 v/P 13 Phenanthrene 0.00002-0.034 v/P 13 Anthracene 0.00005-0.021 v/P 13 Methylan- 0.00007-0.008 v/P 13 thracenes Fluoranthene 0.0007-0.042 v/P 13 Pyrene 0.0008-0.031 v/P 13 Benzo(a) 0.0004-0.002 v/P 13 anthracene Chrysene 0.0005-0.01 v/P 13 Benzo- 0.0006-0.005 v/P 13 fluranthenes Benzo(e)pyrene 0.0002-0.004 v/P 13 Benzo(a)pyrene 0.0003-0.005 v/P 13 Perylene 0.00005-0.003 v/P 13 Ideno(1,2, 0.0002-0.013 v/P 13 3-cd)pyrene Benz(ghi) 0.00005-0.011 v/P 13 perylene Coronene 0.0008-0.003 v/P 13 Dibenzo(a,h) 0.0003-0.001 v/P 13 pyrene Retene 0.007-10.03 v/P 14 Dibenz (a,h) 0.00002-0.002 v/P 13 anthracene Trace Elements Na 0.003-0.018 P 15 Mg 0.0002-0.003 P 15 Al 0.0001-0.024 P 15 Si 0.0003-0.031 P 15 S 0.001-0.029 P 15 Cl 0.0007-0.21 P 15 K 0.003-0.086 P 15 Ca 0.0009-0.018 P 15 Ti 0.00004-0.003 P 15 V 0.00002-0.004 P 15 Cr 0.00002-0.003 P 15 Mn 0.00007-0.004 P 15 Fe 0.0003-0.005 P 15 Ni 0.000001-0.001 P 15 Cu 0.0002-0.0009 P 15 Zn 0.00007-0.004 P 15 Br 0.00007-0.0009 P 15 Pb 0.0001-0.003 P 15 Particulate Ele- 0.3-5 P 16 mental Carbon Norma1 Alkanes 0.001-0.006 P 17 (C24-C30) Cyclic di- and triterpenoids Dehydroabietic 0.001-0.006 P 18 acid Isopimaric 0.02-0.10 P 18 acid Lupenone 0.002-0.008 P 18 Friedelin 0.000004- P 18 0.00002 Chlorinated 0.00001-0.00004 P 19 dioxins Particulate 0.007-0.07 P 20 Acidity ______________________________________
1.Some species are grouped into general classes as indicated by italics. PA0 2. To estimate the weight percentage in the exhaust, divide the g/kg value by 80. This assumes that there are 7.3 kg combustion air per kg of wood. Carbon dioxide and water vapor average 12 and 7 weight percent respectively. PA0 3. At ambient conditions: V=vapor, P=particulate, and V/P=vapor and/or particulate (i.e., semi-volatile). PA0 4. DeAngelis (1980) PA0 5. OMNI (1988) PA0 6.Lipari (1984), values for fireplaces PA0 7. Edye et al (1991), smoldering conditions; other substituted furans include 2-furanmenthanol, 2 acetylfuran, 5-methyl-2furaldehyde, and benzofuran. PA0 8.value estimated for pine from Edye et al (1991) from reported yield relative to guaiacol, from guaiacol values of Hawthorne (1989) and assuming particulate organic carbon is 50% of total particle mass. PA0 9.Steiber et al (1992), values computed assuming a range of 3-20 g of total extractable, speciated mass per kg wood. PA0 10. Khalil (1983) PA0 11. Hawthorne (1989), values for syringol or hardwood fuel; see also Hawthorne (1988) PA0 12. Core (1989), DeAngelis (1980), Kalman and Larson (1987) PA0 13. From one or more of the following studies: Cooke (1981), Truesdale (1984), Alfheim et al (1984), Zeedijk (1986), Core (1989), Kalman and Larson (1987); assuming a range of 7 to 30 grams particulate mass per kg wood when values were reported in grams per gram of particulate mass. Similar assumptions apply to references 14, 15, and references 17-19. PA0 14. Core (1989), Kalman and Larson (1987) PA0 15. Watson (1979), Core (1989, Kalman and Larson (1987) PA0 16. Rau (1989), Core (1989) PA0 17. Core (1989) PA0 18. Standley and Simoneit (1990); Dehydroabietic acid values for pine smoke, lupenone and isopimaric acid values for alder smoke, and friedelin values for oak soot. PA0 19. Nestrick and Lamparski (1982), from particulate condensed on flue pipes; includes TCDDS, HCDDS, H7CDDs and OCDDs. PA0 20. Burnet et al (1986); one gram of acid =one equivalent of acid needed to reach a pH of 5.6 in extract solution.
TABLE 3 ______________________________________ ODOR AND TASTE RECOGNITION THRESHOLDS (ppm) AND MOST DESIRABLE CONCENTRATIONS (ppm) OF THE PHENOLIC FRACTION ISOLATED FROM THE VAPOR AND PARTICULATE PHASES OF WOOD SMOKE Most desirable Recognition threshold concentration ______________________________________ Odor Vapor Particulate Vapor Particulate 10.4 7.8 20.8 16.7 Taste Vapor Particulate Vapor Particulate 2.3 1.4 15.6 8.3 ______________________________________ Adapted from Daun, H., Lebensm. Wiss. Technol., 5, 102, 1972
The seafood or meat treated with wood smoke has myoglobin molecules with open receptors that can undergo a chemical reaction with a variety of compounds present in the smoke--O.sub.2, CO, NO, NO.sub.2 and H.sub.2 O. It is important in cold smoking to keep the meat raw and uncooked to maximize the amount of vital cells available for this reaction. The myoglobin in its natural state is purple. When the myoglobin binds with O.sub.2 it produces oxymyoglobin which is bright red; with CO it produces carboxymyoglobin which is red; with NO and NO.sub.2 it produces nitric oxide myoglobin and nitrogen dioxide myoglobin which are also red; and with H.sub.2 O it produces metmyoglobin which is brown.
Carboxymyoglobin is preferred because of its stable organoleptic freshness characteristics as well as its stable red color. The organoleptic "sniff test" shows significant retardation of decomposition of cold smoked product high in carboxymyoglobin. For example, cold smoked and vacuum packed salmon can be refrigerated for several months without any decomposition.